dioxus/examples/borrowed.rs

#![allow(non_snake_case)]
//! Example: Extremely nested borrowing
//! -----------------------------------
//!
//! Dioxus manages borrow lifetimes for you. This means any child may borrow from its parent. However, it is not possible
//! to hand out an &mut T to children - all props are consumed by &P, so you'd only get an &&mut T.
//!
//! How does it work?
//!
//! Dioxus will manually drop closures and props - things that borrow data before the component is ran again. This is done
//! "bottom up" from the lowest child all the way to the initiating parent. As it traverses each listener and prop, the
//! drop implementation is manually called, freeing any memory and ensuring that memory is not leaked.
//!
//! We cannot drop from the parent to the children - if the drop implementation modifies the data, downstream references
//! might be broken since we take an &mut T and and &T to the data. Instead, we work bottom up, making sure to remove any
//! potential references to the data before finally giving out an &mut T. This prevents us from mutably aliasing the data,
//! and is proven to be safe with MIRI.

use dioxus::prelude::*;

fn main() {
    dioxus::desktop::launch(App, |c| c);
}

fn App<'a>(cx: Context<'a>, props: &()) -> DomTree<'a> {
    let text: &'a mut Vec<String> = cx.use_hook(|_| vec![String::from("abc=def")], |f| f, |_| {});

    let first = text.get_mut(0).unwrap();

    cx.render(rsx! {
        div {
            Child1 {
                text: first
            }
        }
    })
}

#[derive(Props)]
struct C1Props<'a> {
    text: &'a mut String,
}

impl<'a> Drop for C1Props<'a> {
    fn drop(&mut self) {}
}

fn Child1<'a>(cx: Context<'a>, props: &'a C1Props) -> DomTree<'a> {
    let (left, right) = props.text.split_once("=").unwrap();

    cx.render(rsx! {
        div {
            Child2 { text: left  }
            Child2 { text: right  }
        }
    })
}

#[derive(Props)]
struct C2Props<'a> {
    text: &'a str,
}
impl<'a> Drop for C2Props<'a> {
    fn drop(&mut self) {
        todo!()
    }
}

fn Child2<'a>(cx: Context<'a>, props: &'a C2Props) -> DomTree<'a> {
    cx.render(rsx! {
        Child3 {
            text: props.text
        }
    })
}

#[derive(Props)]
struct C3Props<'a> {
    text: &'a str,
}

fn Child3<'a>(cx: Context<'a>, props: &C3Props) -> DomTree<'a> {
    cx.render(rsx! {
        div { "{props.text}"}
    })
}